Method of inhibiting hydrogen sulfide corrosion of metals



Patented May 13, 1952 METHOD OF INHIBITING HYDROGEN SULFIDE CORROSION OF METALS Melvin I. Moyer, Lawrence, Kans., and Joseph M. Hersh, Forest 'Hills, N. Y., assignors to Cities Service Oil Company, Bartlesville, kla., a corporation of Delaware No Drawing. Original application September 11,

1947, Serial No. 773,506. Divided and this application May 10, 1949, SerialNo. 92,502 7 2 Claims. (01. 252-855) Our invention relates to an improved method of inhibiting corrosion of metal, and is more particularly concerned with the treatment of hydrogen sulfide containing brines of the type obtained in the production of crude oil to reduce their corrosive efiects upon oil production and transmission equipment.

This application is a division of our copending application Serial No. 773,506, filed September 11, 1947, now U. S. Patent 2,496,354.

The corrosive action of oil field brines containing hydrogen sulfide in solution has long been recognized as a source of very substantial losses in oil production equipment. In some fields, for example, the brine which is, taken out with the oil is so corrosive in its nature as to be capable of destroying the well tubing with? in a matter of a very few months; and the well casings, separators, pumps, and other equipment with which such mixtures come into contact has a comparably short life.- It has been the practice to utilize caustic soda, soda ash, and other alkaline compounds for neutralizing the acidic components of brines of this general character, and of thereby limiting their corrosive action. These neutralization treatments, however, require the use of comparatively large amounts of the inhibiting agents, are correspondingly costly, and from a long range point of view, have not been outstandingly successful.

The primary object of our invention is to provide an improved process for protecting metals, and particularly iron and steel equipment, used in the handling of crude oil in the presence of the highly corrosive types of brines frequently encountered in oil fields.

We have discovered that oil well tubing and casings, as well as other equipment used in oil production, may be substantially and eiiectively protected against corrosive action of connate brines by mixing with the latter, an organic amino-reactive compound which serves as acorrosion inhibitor. In general we have found that the heterocylic amino-reactive compounds, the alkyl and alkanol amine-aldehyde condensation products of both cyclic and noncyclic types, and

the alkyl-ureas are effective forour purposes;

In accordance with our invention we inject a suitable quantity of a selected inhibitor compound into an oil well and thereby mingle it with the oil-brine production so that the mixture comes into contact with the well tubing, casin and other producing equipment Thus we may introduce the inhibitor into the top of the casing so that it flows down into the well and thence back through the tubing, pumps, collecting lines, etc. In general we have found that this procedure sufiices to protect the entire system of production and collection against corrosion, to a very substantial degree; and far more effectively than treatment with caustic and other inhibiting compounds which have heretofore been used. While introduction of the inhibitor at the well head usually suflices, as has been indicated, it will be obvious that the selected compound may be added to an oil-brine mixture at any point in a system where its presence is required to limit corrosive action. It will further be noted that we prefer to introduce the inhibitor, in liquid form, as an aqueous or alcoholic solution for example, for greater convenience in handling and so that it may more readily mix with and dissolve in the brine to perform its intended function.

The effectiveness of our inhibitors may be better and more easily understood by reference to certain tests which we have conducted upon natural oil field brines containing approximately 40,000 parts per million (by weight) of natural saline solids and about 1,000 parts per million (by weight) of hydrogen sulfide, an analysis which is typical of corrosive brines produced in many fields. The test procedure involved the measurement of the corrosive action of this brine, alone and with our inhibitor compounds,

upon thoroughly cleaned and polished strips of cold rolled steel measuring 4 x inches x 16-18 gauge under conditions which closely approximate those existing in a producing oil well. In carrying out the tests, we filled a series of 16 ounce bottles with natural gas in order to exclude air, and to each added a calculated quantity of one of our amine reactive inhibitors, and then a measured quantity of brine to make up the inhibitor mixture, following which a test strip of known weight was completely immersed in the mixture and the bottles were sealed with rubber stoppers to insure an airtight system. Additional tests were run in other bottles in which the weighed test strips were immersed in uninhibited brine, that is, in the hydrogen sulfide containing brine just as taken from an oil well. All of the tests were run in multiple, both-for the inhibited and the blank solutions, in order to avoid the anomalies of testing. At the end of a test period of about two weeks, the test strips were removed from'the bottles, rinsed with water, and were then' dipped in l per cent hydrochloric acid solution-for ten seconds to remove any light or acid washable film, following 3 which they were successively rinsed in water, dried and weighed to determine the amount of metal lost in the corrosion treatment.

In several series of tests carried out in the manner described above it was observedthat u'n inhibited corrosion weight loss in different brines varied from about 20 mg. to over 1'70 mg. per test" strip while the weight loss of strips subjected to the same brines containing our inhibitors were sharply less. These test data were used to determine the protection numbers; 1. 'e;, the ratio of loss of weight of a strip subjected" to an uninhibited brine to the loss of weight of a strip subjected to the same brine containing our inhibitor, which are reported below in the third column of Table I. For purposes of comparison, we then assumed a weight loss of 100 mg.-fo'r-the uninhibited strip test, and corrected the actual weight losses sufiered by the test strips subjected to the inhibited brines to this assumed basis, thus giving the several weight losses set forthin the fourth column of thetable; i

The results of these tests clearly'indicate' 'that our various inhibitors have a marked effect in reducing metal loss by the corrosive action of hy-' Since these drogen sulfide containing brines. tests were carried out under conditions closely approximating those existing in actual wells, they demonstrate the inhibiting effect which the agents have in protecting oil well tubing, etc. under actual producing conditions.

X Rciaction product of diethanolaminc (2 mols) and formaldehyde 2 Reaction product oi'ethylone diamine (l mol)-and formaldehyde 3 Rclaction product of monoethanolaminefl mol) and formaldehyde The reaction between formaldehyde" and the amines to give the reaction products specified above is well known, and the method of preparing these products is given in Formaldehyde, by J. F. Walker, A. C. S. Monograph Series No l 98, Reinhold Publishing Corporation, New York, 1944, pages200 to 202. g

It will be observed that the foregoingseri'sof tests were carried out in' solutions containing 62 /2 parts of inhibitor compound p'er" million parts of brine, thus giving a basis for evaluating the effectiveness of oneinhibitor with respect to another. The protecting effectivenessof'any of these agents may be varied, however, by iii-- creasing or decreasing the amount employed" in the treating process. I

t may be noted that brines taken from-different wells, even though containing about the same concentration of salt and hydrogen sulfide, may be more or less destructive in their effects upon oil handling equipment. In using our inhibitors, therefore, we find it desirable to adjustth' proportion employed in accordance with" the corro sive character of the brine under treatment. As a general rule, we find that from about m 256 parts-(by weight) of inhibitor, per' million parts (by weight) of brine, is sufficient to assure highly satisfactory protection under normal operating conditions.

At the conclusion of the foregoing tests, and others which need not be specifically considered, it was observed that the metal strips exposed to the uninhibited brines were coated with a thin, fiocculent, gray-to-black material. Doubtless thiscoatinghas some effect in protecting the underlying metal and slowing down corrosive action. 'It cannot be of any great protection value, however, because of its tendency to flake off as is evidenced by thefact that the uninhibited brines were turbid with a grayish fiocculent precipitate,-. even though they had been standing in a quiefstate Tor-approximately two weeks. By way of contrast, the metal strips subjected to the brines containing our amino-reactive inhibitors developed thin but highly tenacious coating which appear to be particularly resistant to hydrogen sulfide brine reaction.

Some-evidence of' the resistant character of thes' films is to be found in the fact that a tenminute treatment in 1 percent hydrochloric acid did not efie'ct complete removal in many cases, andthatthey werenot immediately affected by organic solvents such as alcohol, acetone, ether, methyl-ethyl ket'one, gasoline, benzene, toluene, carbon tetrachloride, and similar solvents.

The inhibiting action of the amino-reactive compoundsis not fully understood but one aspect of theac'tio'n', and the successful protection of metatag'ainst' substantial corrosion, certainly apears" to lie in=the formation of a protecting film upon' the metahas described above. These films may be complex organic'products developed by the a'ct'ion" of the inhibiting agent or its interaction with '3} portion 'of the hydrogen sulfide and brine, in the presence of metal. They ce'rtainl yfare not the result of mere neutralization-of the hydrogen sulfide, as is evidenced by the" presericeof a high concentration of that ingredient-in 'the treated brines. It may be possible; however," that the inhibitor reduces the activityofthe hydrogen sulfide, and other corrosive constituents of the brine. Whatever the nature oftheactior'r may bejthese facts remain clear: A 'filiri is builtup 'o'n'metal surfaces brought into contact-with hydrogen sulfide containing brines which nave seen treated; with amino-reactivecompoiindsin accordance with our inventiofi j and'those films-are resistantboth to mechanical abnasionand" chemical reaction; and that-"tli' prsence oi the compounds in such sentencesverymaterially inhibit corrosion of well tubing, casings, and other oil field equipment carrying-the tr'e edbrines.

It w'ill be'bbsrvdthat the inhibitor compounds are readily obtainable: in high concentration, wnicn erniits economical shipment and handling botl-i in transit"'andin the field;

o e un'derstood that our improved process isnot; n d to' the useofonly one of the inhibitin'g 'compoundsreferred to but the various mixtures of the'inhibitors'may be used in a single operation within the spirit and scope of our invention", Furthermore these corrosion reducing agentsm'ay' beused' alone, or with any other oil welltreating compounds such as those which are conventionally"employed for'breaking emulsions, limiting scaleformation, and the like.

Having" described our invention and illustrated it"by' way or specinc examples, what We claim as new and usemi m 1"-. The processofinhibiting corrosion of metal 5 oil well equipment which comprises introducing into an oil well brine containing dissolved hydrogen sulfide, at a point near a producing horizon of the Well, a small proportion of the reaction product of one mol of ethylene diamine and two mols of formaldehyde, the quantity of the reaction product being sufiicient to substantially inhibit corrosion of the metal equipment and thereafter causing the brine to flow in contact with the metal surfaces to be protected.

2. The method according to claim 1 in which the reaction product is introduced into the brine in the amount of from about 15 to about 250 parts by weight of the reaction product per million parts by Weight of brine.

MELVIN I. MOYER. JOSEPH M. HERSH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1.THE PROCESS OF INHIBITING CORROSION OF METAL OIL WELL EQUIPMENT WHICH COMPRISES INTRODUCING INTO AN OIL WELL BRINE CONTAINING DISSOLVED HYDROGEN SULFIDE, AT A POINT NEAR A PRODUCING HORIZON OF THE WELL, A SMALL PROPORTION OF THE REACTION PRODUCT OF ONE MOL OF EHTYLENE DIAMINE AND TWO MOLS OF FORMALDEHYDE, THE QUANTITY OF THE REACTION PRODUCT BEING SUFFICIENT TO SUBSTANTIALLY INHIBIT CORROSION OF THE METAL EQUIPMENT AND THEREAFTER CAUSING THE BRINE TO FLOW IN CONTACT WITH THE METAL SURFACES TO BE PROTECTED. 